1. Field of the Invention
The present invention relates to a new detergent composition which exhibits superior solubility, detergency, and sudsing not only in soft water but also in hard water, with mild action on the skin and hair, without causing discoloration.
2. Description of the Prior Art
Heretofore, anionic surface active agents which are widely used as the major component of detergent compositions have been supplied at a low price and used in large quantities. These anionic surface active agents are generally functionalized with sulfate groups, sulfoxyl groups, or carboxyl groups. Examples of these anionic surface active agents include: alkylsulfates, alkyl ether sulfates, alkylbenzenesulfonates, .alpha.-olefinsulfonates, sulfosuccinates, higher fatty acid salts, and N-acyl-neutral and acidic amino acid salts. Although these anionic surface active agents are widely used because of their superior sudsing and detergency in soft water and low price, they are useless in hard water where they form water-insoluble scum that contaminates objects being washed.
On the other hand, ampholytic surface active agents, which have both a cationic moiety and an anionic moiety per molecule, are superior in detergency, sudsing, and bacteriocidal and bacteriostatic action, as well as being mild to the skin and eyes. These agents exhibits these characteristics even in hard water. However, their cost makes them economically unattractive to use except in combination with anionic surface active agents.
Detergent composition made up of an ampholytic surface active agent and an anionic surface active agent possess the following merits. (1) The irritation caused by an anionic surface active agent is alleviated. (2) The bacteriocidal and bacteriostatic actions of an ampholytic surface active agent are maintained. (3) The sudsing performance of the composition exceeds that of the individual constituents component. (4) Usually, the critical miscelle concentration is low, and the surface active performance is accomplished at a low concentration. (5) The lack of detergent performance of anionic surface active agents in hard water is prevented to some extent.
According to Linfield, the ampholytic surface active agent, particularly that of the sulfobetaine type, is effective as a lime soap dispersing agent, as reported in "The Journal of the American Oil Chemist's Society", 55; 87 (1978). Despite the above-mentioned merits, detergent composition made up of ampholytic surface active agents and anionic surface active agents have not come into general use because various problems involving the ampholytic surface active agent remain to be solved.
Conventional ampholytic surface active agent are made of an alkylamine. The inevitable amine residues associated with alkylamines impairs the appearance of the product via discoloration. In rare cases, these amine causes allergy. Moreover, many of the conventional ampholytic surface active agents can form addition compounds with the anionic surface active agent, making it necessary to raise the temperature for dissolution. The solution of a mixture of the two types of different surface active agents in certain mixing ratios exhibits viscoelastic properties. (Tsujii et al., The Journal of Physical Chemistry, Vol. 86, No. 8, p. 1437 (1982); and "Yukagaku", Vol. 29, No. 8, p. 562 (1980)).
Mixtures of ampholytic surface active agents and anionic surface active agents have low critical micelle concentrations. This phenomenon is accompanied by a rise in the dissolution temperature and, in some cases, by viscoelasticity (Fragrance Journal, 50; 56 (1981)). These phenomena indicate that in practical applications the mixture of an ampholytic surface active agent and anionic surface active agent yields a product which is not readily soluble in water and which does not exhibit detergency at low temperatures. Moreover, if the mixture is to be used in the form of liquid detergent composition, it will become solid or extremely viscous due to its viscoelasticity. Such a product is difficult to make and inconvenient to use.
For the above-mentioned reasons, detergent compositions made up of an ampholytic surface active agent and an anionic surface active agent have not been commercialized in spite of their inherent advantages.